The Aging of lakes
Publication date 1971
Publisher [n.p.] Encyclopaedia Britanica Education Corp.
Digitizing sponsor Internet Archive
Contributor Internet Archive
Traces the aging process of lakes, showing how man's interference with the environment causes critical changes in the natural ecology. Describes efforts to preserve and restore damaged lakes.
Curatenote color: Good sound: Good synch: Good notes: Film edge is visible on left. Red balance is high.
Ocr Sans. Interference with his environment is causing critical changes in our valuable water resources. One major pollution problem is the increasing nutrient content in freshwater lakes. When. First formed lakes are usually nutrient Corps for all of the tropics. The water is clear as it contains little suspended material or algae. But as time passes. Natural aging occurs and some lakes become nutrient rich or you tropic. Lakes become choked with sediment and living in the Cayenne plants. As layers of sediment and dead plants increase in depth the edge community gradually encroaches out into the shallow water. Over thousands of years. Lakes evolve into bugs or marshes then into meadows and even forests. There are two main causes of Lake aging one is sediment washed into a lake from its tributaries as well as from the lakes on banks. This erosion and the positive sentiment goes on continuously even this clear looking water is carrying some sentiment. The second factor is an increase in dissolved nutrients such as phosphorus nitrogen and carbon. These nutrients cannot be seen. But the plant life they nourish can't miss. This increase in the amount of nutrient in a like is called you Trista cation. The green yellow or brown tent in water is caused by algal blooms. When these plants die they contribute to Lake aging nutrients are continuously recycled so that more plants grow die and decompose using more and more of the oxygen in bottom waters. Consequently species of fish with higher oxygen requirements are unable to survive. They are replaced by species with lower oxygen requirements. As the amount of dissolved oxygen continues to decrease. Car and other roughish replace more desirable species. Slow you drip occasion can be beneficial in increasing the productivity of the lake. But in many cases you trip occasion is accelerating at an alarming rate. This can be detected by measuring transparency and dissolved oxygen content. As you traffic a sion progresses transparency lesson once and dissolved oxygen decreases in the bottom waters. Looms of algae cause taste odor water filtration and other problems. The increased rate of you driven cations seems to be directly related to the growth of man's population around lakes. This graph shows that the population around Lake Michigan has steadily increased since eighteen forty. There has been a corresponding increase in dissolved solids in the lake. A similar correlation exist in the other Great Lakes. The conclusion is obvious. Man substantially contributes to and speeds up the natural aging process. Domestic sewage contributes large amounts of nutrients such as phosphorus detergents had been a major source. Additional phosphates come from farm wastes and fertilizers washed from fields. You drop a conditions caused by industrial pollution are being reported worldwide. In large cities where most land has been paved or built on little rain soaked into the ground. Raindrops pick up dust so it pollen and gases from the atmosphere. Boils Grace animal wastes and other debris as well are washed away. In most large cities the same sewer that carries raw sewage from homes and offices to the sewage treatment plant is also used to carry off storm water. When heavy rains occurred sewage treatment plants cannot handle the extra load. So raw sewage is diverted to lakes or rivers along with the rainwater. The accelerated input of nutrients. Speeds up you trip occasionally and upsets the ecological balance. Algae and other plants grow profusely. Bacteria and chemicals flushed into the water use up dissolved oxygen. Fish and other animal life diet. A lake. Transformed into a smelly on sanitary mess is often said to be biologically dead that. In truth this water is very much alive biologically. There are astronomical numbers of algae and a wide variety of the composers. Some fish that can tolerate low oxygen levels still survive. A tragic result of accelerated ageing is the loss of one of man's most valuable resources. Many communities and government agencies are turning their efforts to reducing your terrific Asian for slow down the aging process here a lake is being dredged to remove nutrient its settlements which of clogs it's the it's. The sediment and other debris are pumped on to land where they are used as landfill. Some nutrients can be removed from a lake by cutting and removing the weeds in which they are contained. After harvesting the weeds might be a future source of fertilizer or cattle call. Let's like is being pumped up in the highly lucrative waters are being spread out on the surrounding land. The lake will refill itself from underground springs that's getting a fresh start. In another every artificial Ericsson is being tried to increase dissolved oxygen content. Compressors furnish the air which is pipe to several underwater outlets far out in the lake. Turbulence caused by the escape of their increases the dissolved oxygen content in the bottom water. This communities lake is small but highly prized. Here people are contributing their time to clean out years of accumulated debris. Later the lake will be drained so that its bottom can be covered with black plastic sheeting weighted with gravel. This will help keep the nutrients trapped below. All of these efforts should help slow your vacation but they are treating it symptoms not as far as. The only long range solution is preventing man made pollutants from entering our lakes. Commonly used secondary treatment of sewage removes only part of the nutrients until treatment methods are improved the best solution would be to divert sewage away from Lee. As early as one thousand nine hundred to reduce the problem of water borne diseases such as typhoid from contaminating its water supply. Chicago constructed locks to reverse the flow of the Chicago River. This diverted sewage wastes from Lake Michigan and it's kept lakefront water is relatively clean. Treated sewage and storm drainage now flow into a natural and artificial river system where continuous flow in mixing can better handle the incoming wastes. Seattle Washington and surrounding towns dump sewage into Lake Washington for many years. The nutrient rich sewage caused a tremendous growth of slimy algae. The lake became unsafe to swim in and unpleasant for voting. Beginning in one nine hundred fifty seven new networks of pipelines and sewage treatment plants were built to divert the waste water away from the lake and into the offshore waters of the ocean. Lake Washington is a good example of how even a very large lake can be rehabilitated from high you trough the conditions. But even though the treated waste water is of Chicago Seattle in most other cities are piped elsewhere they still carry high concentrations of nutrients into rivers and oceans. A third stage of sewage treatment is needed to correct this condition. In this tertiary treatment plants. Solids that remain after regular secondary treatment are removed by sand filtration and micro straight. Various means can be used to remove dissolved nutrients oxygen is put back in the water by bubbling air through. The treated water now ready for discharge from the plant. Meets the standards of the Federal Water Quality Act of one thousand nine hundred five. Sludge a byproduct of sewage treatment plants cannot be dumped into streams but it can be used as a natural fertilizer. This land reclamation project demonstrates how nutrients contained in sludge can convert unused land into fertile crop bearing far Marion's. Flood Control reservoirs are a way of retaining stormwater is until they can be released on a regulated basis following the storm. Deep underground tunnels such as this one being built in Chicago will be able to hold back millions of gallons of storm water that would otherwise flooded basements and wash on treated waste into Lake Michigan. Much needs to be learned about how man's activities affect you. Terrific casing. Here are sites of nuclear power plants built to our proposed on Lake Michigan alone. How will the discharge of heated water thermal pollution from these plants. Effect Blake aging. While all lakes are destined to age and die of natural you trip occasion is a slow process. Usually taking thousands of years for even the shallow small lakes we can reduce man's contribution to you. Terrific a shim by applied research and technology if we will expend the effort and money. What works in one like at its surrounding area might not work elsewhere. Each lake has its own problems. Lakes are a prized resource of manner but it's like as an entity with its own ecology. Its problems must be dealt with accordingly. Sir. This.
Run time 13:44
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